Making elastomer containing paper



Patented Apr. 14, 1953 MAKING ELASTOMER CONTAINING PAPER Andrew LoyMoore Bixler, Milford, N. J., and Jacob I. Fisher, Easton, Pa.,assignors to Riegel Paper Corporation, New York, N. Y., a corporation ofNew Jersey No Drawing. Application April 21, 1948, Serial No. 22,498

15 Claims.

This invention relates to improvements in the manufacture of paperhaving elastomeric materials incorporated therein, and more particularlyto the production of a strong, tough and pliable sheet of paper with ahigh initial tear strength, with a soft, leather-like feel and with goodabrasion resistance.

The invention includes an improved method of producing such paper andthe improved paper resulting therefrom.

The invention includes an improved method of incorporating elastomericmaterials to the extent of about 20% to 50% in a sheet of paper byprecip-itating emulsions of elastomeric materials in paper pulp which,instead of having ordinary beater consistencies of around 3 to 5% fibersolids, is diluted to a consistency of around 1% of fiber solids beforethe addition of the emulsions and the precipitation of the elastomericmaterials therefrom; and in which the protective colloid materials areassociated with the fibers, rather than with the emulsion, before theemulsion is admixed with the paper pulp and. the elastomeric materialsprecipitated therefrom.

The invention includes further improvements in the process of makingsuch paper in which the protective colloid materials, and advantageouslyalso part or all of the alum for precipitating the elastomeric materialsfrom the emulsions, are in-.

corporated in the pulp in the beater at ordinary beater consistenciesprior to dilution of the pulp to a consistency of around 1 and. theadmixture of the emulsions of elastomeric materials therewith.

The invention includes process steps whichare advantageously utilized incombination in producing the improved and superior, tough, pliable sheetof paper with a high initial tear strength.

The process of making paper having elastomeric materials incorporatedtherein by precipitating rubber latex or synthetic rubber latex oremulsions of elastomeric materials in paper stock is a known process. Itis also well known that 2 a strong, tough, pliable sheet of paper may bemade.

One of the chief physical properties desired in this type of paper isknown and referred to in the paper trade as initial tear or edge tear.The improved process of the present inventionresults in the productionof a superior sheet of paper having high initial tear strength as wellasa soft, leather-like feel and good abrasion resistance.

Paper pulp or stock at ordinary beater consistencies contains around 3to 5% of fiber solids in the fiber-water suspension.

While it is possible to obtain fair results by the use of such beaterconsistencies at the time of precipitation of the elastomeric materialfrom the emulsions, we have discovered that paper with superior physicalproperties can be made by precipitating the rubber at a stockconsistency of about 1 We have found that a consistency of about 1%appears to be an optimum condition for the precipitation. We have foundthat the maximum physical properties were obtained in the range of fromA; of 1% to 1 consistency, with best results at 1%; and thatprecipitation at materially-higher or lower consistencies than thesegave distinctly inferior properties to the paper.

We have also'found that it is important, for best results, to associatethe protective colloid materials with the fibers rather than with theemulsion before it is admixed with the fibers. This is contrary to thepresent procedure and to the commonly accepted teaching of the art thatit is the emulsion particles which should be associated with theprotective colloid materials before they are admixed with the paperstock. When the present practice is used, and the protective colloidmaterials areincorp'orated in the emulsion, an apparently uniformprecipitation can be obtained without objectionable clotting of thefibers; "but the precipitation of'the elastomeric material, though'it bein the form of a fine flock, Will not be firmly and completely attachedto the the ordinary emulsions of this kind, whenpre- 'cip-itateddirectly with a coagulant such as alum,

tend to come out in the stock as balls or agglomcrates of stickymaterial, whereas it is desirable that the rubber be precipitated in theform of a fine flock. If the elastomer comes out and forms balls orclots of fibers it is notuniformly distributed on the fibers even thoughthe precipitate be finely divided and evenly distributed. The purpose ofincorporating elastomeric materials in paper pulp and of producing paperhaving elastomeric materials incorporated'thereinis .50 that fibers anda product of inferior physicalproperties is produced. g

The amount oflatex or-elastomeric emulsion used in making thenew papercan be varied to give paper containing from about 20% to about 50%. Anamount of about 30% in the paper is advantageous. Above 30% only slightadditional strength or toughness is attained, but improved resistance topenetration is obtained,.which is advantageous for certainuses. Below20% the strength and toughness drop off rapidly. Such an amount of latexor elastomeric emulsion corresponds to from about 25% to about 100% ofelastomeric material based on the dry weight of the fibers of the pulpto which the latex or emulsion is added to give paper containing fromabout to about 50% of elastomeric material.

The improved process of the'present invention will be furtherillustrated by the following specific example:

Example 1.--100 lbs. of unbleached kraft pulp were beaten to 700 cc.freeness Canadian) in an ordinary paper mill beater. This was done atordinary paper-making consistency. (3 :to "5%) The stock was thenemptied to a chest and diluted to 1% consistency and the'followingchemicals were added as colloid protectives: 1 lb. oxalic acid dissolvedin 2 gallons of water; 1 lb. sodium hydroxide dissolved in 2% gallons ofwater;

2 lbs. sodium silicate syrup (special brand) dis- I solved in 2 /2gallons of .water; .75 lb. alpha protein dissolved in cc.s of ammoniumhydroxide in 2V2 gallons of water; '7 .2 lbs.of ammonium hydroxide(28.9%). These chemicals were thoroughly mixed with the fiber watersuspension and then the elastomeric emulsion was added. In this case 154 lbs. of 27.8% solids synthetic (acrylonitrile-butadiene) rubber latexwere used.

After the rubber emulsion was thoroughly mixed, alum was added tocoagulate the rubber. The alum was added as a 2% solution andabout 13lbs. was necessary for complete coagulation. The preferred method was toadd it in steps of 2 lbs. at a time, allowing 5 minutes betweenadditions. Thorough mixing was obtained after and during addition. Assoon as the precipitation was complete, the stock was ready to run onthe paper machine.

In the above example the pulp was diluted from ordinary paper makingconsistencyto about 1% consistency before the incorporation of theprotective-colloids therein. We have found, however, that the protectivecolloid materials can advantageously be added to the stock in the beaterat ordinary beater consistencies (e. g., around 3 to 5%) and that thedilution to 1% consistency can then be made and followed by the additionof the emulsion and precipitation by alum. This procedure is moreadvantageous for mill operation, while the paper produced isnevertheless paper of the desired improved physical properties.

As an illustration of the improved im'tial tear strength of the paperobtained when the latex or elastomeric emulsion was precipitated at aconsistency of 1%, according to the above example, we give below theresults obtained with such .5 precipitates in comparison with theresultsobtained when the latex or elastomeric emulsion was precipitated at 4%consistency.

It is evident from the above data that the initial tear is very muchsuperior when the latex or elastomeric emulsion is precipitated in thepaper pulp at 1% consistency than it is at 4% consistency.

The theory and exact mechanism of the efiect of consistency on theprecipitation of elastomerio materials from emulsions in paper stock, asabove illustrated, and the reason for the improved results obtained atthe optimum consistency of around 1'%, is not yet clearly understood;but the marked improvement in results has been demonstrated. Microscopicstudies of the fibers indioate'that .at the :optimum consistency ofabout 1 1% the precipitated elastomeric particles are evenly distributedand firmly attached to the fibers. Elastomeric materials precipitatedmaterially outside of the optimum consistency range show under themicroscope more spotty distribution and poor adhesion to the fibers. Atthe optimum consistency the water in the slurry becomes completelyclear, indicating that the elastomeric material has been finely attachedto the fibers; whilemateriallyoutside the optimum consistency range thewater of the slurry tends to remain turbid, apparently because theelasto meric precipitate is not completely attached to the'fibers, inwhich case the retention of the elast-omeric precipitate in the sheet isdependent to a considerable degree on the filtering action as thensheetis being formed. In the optimum range, where the elastomeric material isfirmly held by the fibers, apparently by some physical phenomenon, theretention of the elastomeric particles is much more positive than thatobtained by simple filtering action.

While we do not desire to limit ourselves by any theoretical explanationof the mechanism or mechanics of the precipitation process, we have beenled to believe that when the consistencies are materially below of 1%,the emulsion solids will precipitate mostly or to a considerable extentin the water; while with consistencies of about 1% we are led to believethat the area of total fiber exposed will be such as to allow theemulsion solids to cover each fiber evenly and that when this conditionexists each individual fiber adds to the final strength of the sheet. Asthe consistencies rise above the optimum we are led to believe that theprecipitated rubber present does not get on the fibers evenly and coatsonly part of the fiber surface present, e. g., around l0 to withresulting lowering of the strength of the sheet formed. It may be thatthe optimum consistency of about 1% issuch that the fibers are so spacedapart as to promote uniform and efiective precipitation of the emulsionsolids on .or in such Basis Initial Tear Hand Precipitating Weight Gaugein Tensile, Percent Factor Tear consistency 3,000 Inches p. s. i.Stretch (Tensile X Evaluasq. ft. Stretch) tion 1.0% 162 16. 5/1, 000 2,15. 4 33, 000 .Good. 4.0% 21/1, 000 1, 474 6.0 8, 850 P001.

intimate contact with the fibers as to give a resulting stock withthefibers so oriented therein and so intimately coated with the fineprecipitated elastomer particles as to give the improved propertieswhich we'have observed are obtained in such cases.

The process describedin the above example requires effective andthorough agitation during 75 precipitation and a slow or stepwiseaddition of the alum.. While the improved paper of high initial tearstrength can be produced in this way, we have foundthat the process canbe further improved and simplified and paper of the desired superiorproperties obtained by adding both the protective colloid materials andthe alum for partial precipitation to the beater while the stock isatbeater consistency of around 3 to 5%. The amount of alum thus added isadvantageously about one-half to four-fifths of the alum required forprecipitation. This alum is added to the beater after the addition ofthe protective colloid materials and after these have been well mixedwith the stock. This alum can be added as a solution all at one step. Werefer to this as the pre-alum addition.

After the pre-alum is well mixed and distribbodiment of the process thealum can be added dry and need not be dissolved in water before theaddition to the protected stock. And we have found that this modifiedprocess is in certain respects a more simplified process and one betteradapted to practical mill scale operation, and is uted throughout thestock, the protected stock is I dumped from the beater to a chest anddiluted to 1 consistency and the emulsion is then added and allowed tomix for about 15 minutes. pending on the quantity of the pre-alum used,the elastomeric material is more or less precipitated during this mixingperiod. An advantageous method of procedure is to add suiiicientpre-alum to precipitate about 80 to 90% of the emulsion solids. Theremaining 10 to is then precipitated by further addition of alum addedslowly as a 1 solution.

The process carried out with the addition of both the protective colloidmaterials and the prealum to the beater before dilution is illustratedby the following example:

Example 2.-100 lbs. of unbleached kraft pulp were beaten to 700 cc.freeness (Canadian) in an ordinary paper mill beater at 4% consistency.The following chemicals were thenadded: 1 lb. oxalic acid in 2 gallonsof water; 1 lb. sodium hydroxide in 2 gallons of water; 2 lbs. sodiumsilicate syrup (special brand) in 2 gallons of water; .75 lb. alphaprotein dissolved in cc.s of ammonium hydroxide in 2% gallons of water;7.2 lbs. of ammonium hydroxide (28-29%); and 10 lbs. alum dissolved insufiicient water to make a 10% solution. After 10 minutes mixing, the

stock was dropped from the beater to a chest and diluted to 1%consistency, then 154 lbs. of 27.8% solids synthetic rubber latex wereadded. After 15'minutes mixing, 3 lbs. of alum were added slowly butcontinuously as'a 1% solution. This completely precipitated the rubberlatex and the stock was run over the paper machine, giving paper withsuperior physical properties.

Where alum is added following the addition of the emulsion ofelastomericmaterials, as in the processes above described andillustrated'by the foregoing examples, it is important to insure rapidand thorough agitation. While this prob lem is minimized by the additionof most'of the" alum prior to the addition of the emulsion, it is stillnecessary'to have rapid and thorough agitation "during the addition ofthe small final portion of alum, after the addition of the emulsion, tocomplete the precipitation. In the practical carrying out of theprocess, theagitating'equipment provided in chests may not producesufficiently rapid and thorough agitation, since the normal operation ofpaper mill chests does not require such agitation. The provision ofsupple'-.

mental equipment to produce suchagitation involves added expense andmore power for its operation than the usual lower speed equipment.

We have found, however, that our improved process can be carried outadvantageously to proagitating our preferred and more practical andadvantageous process.

In this improved process, in which all of the alum is added for completeprecipitation of the emulsion, prior to dilution and addition of theemulsion, it is important that the quantity of alum required bedetermined by preliminary test, particularly as the necessary quantityof alum is somewhat flexible and varies with other factors whichinfluence it. Thus the time, the temperature, and the degree ofagitation allhave infiuence on the quantity of alum required, all otherfactors being constant. This necessary quantity can be readilypredetermined by test, using the pH of the stock as a measure of theamount of alum'req'uired, under the combination of other conditionsexisting, and maintaining the pH within narrow limits in carrying outthe process.

The range of pH in which most satisfactory results have been obtained inboth laboratory and commercial runs has been from about 5.0 to about6.5, although this range does not appear to be a limiting range. We havefurther found that when the necessary quantity of alum has beenpredetermined by test, and the' corresponding pH determined, it isimportant to control the pH within approximate 0.2.

The rate of precipitation, and the time required for completeprecipitation, when all of the alum is added before dilution and beforethe addition of the rubber latex, are important for best results. tendsto cause the rubber to come out in large particles which are not firmlyattached to the fibers so that a sheet of inferior strength is produced.Too slow a rate of precipitation tends for a shorter or longer time. Therate of precipitation is also effected by other factors, such as thetemperature, the degree or rate of agitation, the kind of protectivecolloid material used, and the quantity of protective colloid materialused. However, these variables, while varying in different plants andunder different conditions, will or dinarily be more or lessstandardized so that a preliminary test, under such standardizedconditions, will enable the amount of alum required, and thecorresponding pH of the stock (1%), to be predetermined so that the rateof precipitation can be controlled byfcontrollin'g the pH of the stock,within rather narrow limits when the amountof alum andthe'c'orresponding pH have beenso predetermined. The effect on the rateof precipitation by'any of :the other factors can be A too rapid rate ofprecipitationetep nseiediee rnm to beadded' to-determine the properrateof pre. cipitation For example, under one condition of agitation andtemperature, a pilot 5.4 may correspond to the. quantity of alumrequired to give, the proper rateof precipitation; while atanothercondition of agitation and temperature. the same or proper rate'of precipitation may. be. achieved at a pH of 6.2

he l aeiiir t lunInui I asset w en. to predetermine: the necessaryquantity of alum with the emulsion before it is added-to the paper,-are. shown by theiollowing data, which illustratev .the improvedinitialtear strength obtained when all the protective .colloidmaterials, were added to the;fiber slurry incomparison with theresultsobtainedwhen only half of the protective colloid materials wereadded to the latex or elastomer emulsionbefore it was admixed with thefiber slurry. All the other chemicals were added to the pulp as in theexamples. In both cases the stock consistency was 1 Treatment nd TearEvaluation Initial Tea Factor (Tensile X Stretch) Basis Wt.

93% q Percent Gauge in A Tensile,

' Stretch Inches p. s. 1.

All 1protectives added to fiber urry Half of 'protectivcs' added tolatex Good.

Fair.-

sistency. The following chemicals were then added: 3 pounds of oxalicacid as 16 solution in water; 3-pounds sodiumhydroxide dry flake; 18pounds sodium silicate syrup, (special brand) as received;2%,poundS-alpha; protein dissolved in 75 co, ammonium-,hydroxidedn 1'7pounds of water; (28-29%.NH3); and-64.-5-pounds of alum, dry ground.Fiveminutesimixing time was allowed between each addition.- Ten minuteswas allowed following the addition of the alum for complete solutionand; mixing. Th stock was then diluted to 1% consistency anddropped;toachestwith- 648pounds of ;20%- solid ssynthetic rubber latex. Thelatexwas poureddown the drop line as the stock was going down; Thisgives rapid and, thorough mixinglof the latexwith the completelybuffered stock Theprecipitation was completedin 20 minutes ,from;the-timeof addition of the rubber. The-pI-Iof the bufiered stock at 1%con sistency just betore; the ,latexwas added was 5.2.

he. paper produce finl cord w th: b v e a plewasi eeef om bi etion bepart les of 7 rubber and had:the;snperior.;physical properties, I

especially high initial or edge ,teanshown -by -E xamples l and 2. The-following data are repre-. sentative 1 of paper. made; in accord; withEx pleB;

added thereto, as, pqmpared med heai rot qtireemai ais are-r ined.

20.5 pounds of ammonium hydroxidev The i r v d esa ie'ntt ineqtb w heroc in -whichthe protective ,colloidrr aterial are add ed to the fiber,suspensiombefore. the .emulsion is an t ults 0 l.

The states aballatex Had-s the as..

examples to produce paper containing about 30%- of rubber was a latex ofsynthetic. rubber of the butadiene acrylonitriletype known to the tradeas Hycaror Xylos rubber. Such a synthetic rubber latex givesa. resultingsheet of 7 paper with high initial tear. The type of rubber latex to beused in carrying out the process of the invention, as well'as theamount,,can, however, be variedandwill depend on the various propertiesdesired in the finished sheet. Synthetic rubber latex of the typeindicated is also advantageous where greaseproofness or oilproofness isrequired such as for gaskets. Other types of dispersions withelastomeric properties canbe used; such as butadiene-styrene, neoprene,polyvinyl chloride, vinyl copolymers, nylon, and natural rubber,depending onthe particular properties desired in the composite.paperelastomer sheet. Improved elastomeric properties-maybeobtained ;bythe addition of suitableplasticizers "with-the resin, if so desired.

The examples given have referred to unbleached kraft pulp. Our inventionis not, however, limited to this pulp. Otherpulpssuitable for papermaking are included. Some such pulps are-the various wood pulps(sulfite, krait, soda, semichemical, groundwood, etc), rag pulp, ropepulp, jute pulp, etc. pulps are included. The exact choice of pulp andwhether or not it is bleached will depend-on the properties desired .tofulfill thefinal use re-.

quirements of thepaper;

Variations can be made in theprocess from the formulas and procedures ofthe above examples, which are intended to be illustrative but notlimiting; Thus, for example, other colloid ma-.

terials than alpha protein-can be usedsuch as, for exampl e,-hemoglobin, casein, starch, sodium alginate, etc., and these may be usedin conjunction with or as substitutes for the alpha protein.

This invention includes inits scope various modificationswell knownamong paper makers and which modification might add desiredpropertieS-for various special uses. Examples ofsuch wellknown-modifications that might be useful are-sizing for water resistancewith'rosin, synthetic resin or wax, application of materials to producewet strength;coloring,-filling, calendering, embossing,.etc.;

It i usbe seent at he re ent v t o p ov es i prpvedrroq see r. e prduction ofa superior, tough, pliable paper sheet with high initialtearstrength, It'will; alsobe seen that ei r nt oniecludes P oc ss stepsand f a r s Bleached or unbleached which can advantageously be used incombination with each other. It will further be seen that the improvedprocess of the invention results in the production of a new and superiorsheet of paper which is strong, tough and pliable and which ischaracterized by high initial tear strength, a soft, leather-like feeland good abrasion resistance.

We claim:

1. In the method of making a tough, pliable sheet of paper with a highinitial tearstrength, having about to 50% of elastomeric materialsincorporated therein, the step which comprises precipitating by theaction of a dilute solution of alum the elastomeric material onto thefibers of a slurry of fiber and water containing an emulsion ofelastcmeric material and a protective colloid material, while saidslurry has a fiber consistency of about 1%.

2. The process according to claim 1 in which the protective colloidmaterial is added to the fiber water slurry prior to the additionthereto of the emulsion of the elastomeric material.

3. The method according to claim 2 in which the precipitation of theemulsion in the slurry is effected by the stepwise addition of an alumsolution containing about 2% of alum solids.

4. The method according to claim 2 in which a portion of the alumnecessary is incorporated in the fiber Water slurry following theaddition of the protective colloid materials and prior to the additionof the emulsion of elastomeric material, the remainder of the alumnecessary for precipitation being added following the addition of theemulsion of the elastomeric material, this last portion of the alumbeing added in dilute solution of about 2% solids concentration and in astepwise manner.

5. The method according to claim 2 in which about four-fifths of thealum necessary is incorporated in the fiber water slurry followin theaddition of the protective colloid materials and prior to the additionof the emulsion of elastomeric material, the remaining one-fifth of thealum necessary for precipitation being added following the addition ofthe emulsion of the elastorneric material, this last portion of the alumbeing added in dilute solution of about 2% solids concentration and in astepwise manner.

6. The method according to claim 2 in which all of the alum necessaryfor precipitation is incorporated in the fiber water slurry followingthe addition of the protective colloid materials and prior to theaddition of the emulsion of the elastomeric material.

7. The method according to claim 2 in which 'all of the alum necessaryfor precipitation is incorporated in the fiber water slurry followingthe addition of the protective. colloid materials and prior to theaddition of the emulsion of the elastomeric material, and in which a pHof from about 5.0 to 6.5 is maintained in the slurry when the emulsionof elastomeric material is added.

8. Ijhe method according to claim 2 in which all of the alum necessaryfor precipitation is incorporated in the fiber water slurry followingthe addition of the protective colloid materials and prior to theaddition of the emulsion of the elastomeric material, and in which thequantity of alum incorporated in the fiber water slurry is such as toeffect precipitation of the elastomeric material from the emulsion infrom 15 to '45 10 minutes after the addition of the emulsion to thecompletely buffered fiber water slurry.

9. In the method of making a tough, pliable sheet of paper with a highinitial tear strength having about 20% to 50% of elastomeric materialsincorporated therein, the steps which comprise adding protective colloidmaterials to a prepared paper stock at normal beater consistency (about3-5%), diluting the stock to about 1% consistency, adding an emulsion ofthe elastomeric material to the diluted stock and precipitating theemulsion in the slurry while it is at said diluted consistency by theaction of a dilute solution of alum.

10. The method according to claim. 9 in which at least part of the alumis added to the stockbefore dilution and before the addition of theemulsion of elastomeric material.

11. The method according to claim 9 in which all of the alum necessaryfor precipitation is incorporated in the fiber water slurry at normalbeater consistency, and the slurry is subsequently diluted to about 1%consistency before addition of the elastomeric material.

12. In the method of making a tough, pliable sheet of paper with a highinitial tear strength having about 20% to 50% of elastomeric materialsincorporated therein, the steps which comprise preparing a paper stockof from about 3 to 5% consistency, adding protective colloid materialsthereto, subsequently adding alum thereto, diluting the stock to aslurry of fiber and water having a fiber consistency of about 1%, addingthe emulsion of elastomeric material to said slurry and precipitatingthe emulsion therein while it is at said dilute consistency by theaction of a dilute solution of alum.

13. The method according to claim 12 in which alum is also added to thediluted slurry.

14. The method according to claim 12 in which from one-half tofour-fifths of the alum required for precipitation is added prior to theaddition of the emulsion and in which a solution of about 2% alum isgradually added after the addition of the emulsion to complete theprecipitation.

15. The method according to claim 12 in which I all of the alumnecessary for precipitation is incorporated in the fiber water slurry atnormal beater consistency, and the slurry is subsequently diluted toabout 1% consistency before addition of the elastomeric material.

ANDREW LOY MOORE BIXLER. JACOB I. FISHER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,773,201 Rose Aug. 19, 1930 1,799,217 De Cew Apr. 7, 19312,041,968 Schur May 26, 1936 2,215,553 Johnson Sept. 24, 1940 2,330,084Scott Sept. 21, 1943 2,474,801 Owen June 28, 1949 FOREIGN PATENTS NumberCountry Date 375,845 Great Britain June 30, 1932 402,982 Great BritainDec. 14, 1933 OTHER REFERENCES India Rubber World, Feb. 1, 1923, page283.

1. IN THE METHOD OF MAKING A TOUGH, PLIABLE SHEET OF PAPER WITH HIGHINITIAL TEAT STRENGHT, HAVING ABOUT 20% TO 50% OF ELASTOMERIC MATERIALSINCORPORATED THEREIN, THE STEP WHICH COMPRISES PRECIPITATING BY THEACTION OF A DILUTE SOLUTION OF ALUM THE ELASTOMERIC MATERIAL ONTO THEFIBERS OF A SLURRY OF FIBER AND WATER CONTAINING AN EMULSION OFELASTOMERIC MATERIAL AND A PROTECTIVE COLLOID MATERIAL, WHILE SAIDSLURRY HAS A FIBER CONSISTENCY OF ABOUT 1%.